This invention relates generally to actuated mechanical interlock mechanisms and, more particularly, to high stability latching of deployable optical metering structures.
To extend the range of astronomical telescopes, it is necessary to increase the effective aperture. This implies that larger diameter primary mirrors must be employed. Unfortunately, the current state of the art is at the practical size limit of monolithic mirrors. As a result, segmented primary mirrors comprising a plurality of petals surrounding a monolithic center segment must be devised. A space born telescope of this configuration will require deployment after being placed in orbit. Linear, stable, high stiffness precision latches must be used to interlock the metering structure once the mirror is deployed to maintain mirror performance. Current latching technology does not address the need for high stiffness, linearity, and precision. Latch technology as used in satellite antennae does not meet optical tolerance requirements. Their repeatability and stability are typically two orders of magnitude below optical system requirements.
Latching mechanisms commonly found can be categorized either as a retaining type or a mating type. Retaining types are preset in the latched position and release in their operating state. Examples of this type are illustrated in U.S. Pat. No. 4,682,804 to Palmer, et al. and U.S. Pat. No. 4,508,296 to Clark. These devices are used to retain payloads during transport, preventing damage due to shock and vibration. Remote release of the latch allows the payload to be removed from the support structure. High reliability and preload are their key performance requirements.
Mating type latching mechanisms are illustrated in U.S. Pat. No. 4,431,333 to Chandler and U.S. Pat. No. 4,905,938 to Braccio et al., 1990. These devices have male couplings that mate with female sockets. Latching occurs after the halves are mated and serve to connect two bodies after contact. These are used to grapple satellites for repair or connection of trusses where only low tolerance alignment is necessary. Again no consideration is given to dynamic performance of the connection.
It is therefore an object of the present invention to provide a linear, stable, high stiffness precision latch mechanism.
It is a further object of the present invention to provide a precision latch mechanism with high repeatability and stability.
Yet another object of the present invention is to provide a latch mechanism for use in the deployment of a segmented primary mirror comprising a plurality of petals surrounding a monolithic center segment.
Still another object of the present invention is to provide a precision latch mechanism that can be used to interlock the metering structure of a segmented mirror once the mirror is deployed to thereby maintain mirror performance.
Briefly stated, the foregoing and numerous other features, objects and advantages of the present invention will become readily apparent upon review of the detailed description, claims and drawings set forth herein. These features, objects and advantages are accomplished by providing a high stability ball-in-cone type latch mechanism designed specifically for large deployable optical systems. It provides a nearly perfect kinematic mount between structural or optical elements and can easily be remotely controlled. Clamping force and drive position feedback can be incorporated to allow controlled closure and continuous force monitoring during and after clamping. When in the closed position, the interface consists of a ball captured between two conical surfaces. A flexured ball and floating clamp plate is typically attached to the structure being deployed. The latch base is equipped with a conical seat to accept the ball, and three clamp fingers to grip the floating clamp plate once the ball is seated in the socket. A lead screw driven axial cam serves to drive the clamping mechanism into both a clamped and a retracted position. A four bar linkage is formed by the latch cam, coupler link, follower link, and seat. Once the follower link is grounded on the seat, the coupler link acts as a simple lever applying force to the clamp plate. Advantage is taken of the relatively large motion available from a four bar mechanism, as well as the mechanical advantage of a simple lever once latching is initiated. Large clamping forces generated at the interface by the coupler are reacted at the seat thereby providing high interface stiffness and linearity. No latching forces are transferred to the optical support structure. High interface clamping forces on the order of 1000 lbs. can be achieved with low input torque at the lead screw by choosing appropriate cam angles. Employing a flat cam area at the end of travel eliminates the need for accurate final cam position. Choosing appropriate materials can eliminate thermally induced force variation. End mounting the lead screw in the latch seat with a spherical bearing compensates for part tolerances, equalizing clamp finger force during latching. Limit sensors at extremes of cam travel and strain gauges on clamp arms can be provided to monitor operation during the latching procedure.